The subject matter disclosed herein relates to circuit breakers and, more particularly to a circuit breaker crossbar assembly.
Multi-phase industrial electrical power distribution systems are protected against damage from overcurrent circuit conditions by corresponding single or multi-pole circuit breakers wherein each phase of the power distribution circuit is directed through a separate pole within the circuit breaker assembly. The overcurrent situations may be caused, for example, by short circuits or ground faults in or near such equipment. A circuit breaker may be manually switched from an “ON” condition to an “OFF” condition and vice versa. Additionally, the circuit breaker typically includes a mechanism that is configured to automatically switch the circuit breaker to an “OFF” (e.g., “TRIP”) condition in response to an undesirable operating situation, such as a short circuit, for example.
Circuit breakers typically include at least one pair of separable main contacts housed within a housing which typically comprises a base and a corresponding cover. The separable contacts may be operated either manually by way of an operating handle disposed on the outside of the circuit breaker housing and in operative communication with an operating mechanism disposed within the circuit breaker housing, or automatically in response to an overcurrent condition. In the automatic mode of operation, the contacts may be opened by an operating mechanism, controlled by a trip unit, or by magnetic repulsion forces generated between the stationary and movable contacts during relatively high levels of over current. Because of the potential for damage caused by the overcurrent conditions, it is desirable to trip the circuit breaker as rapidly as possible to interrupt the current flow through the circuit breaker.
Typically, the at least one pair of separable main contacts comprise a moveable contact and a stationary contact, wherein the moveable contact is selectively moved by the operating mechanism between the ON condition in contact with the stationary contact, and the OFF position separate from the stationary contact, and vice versa. The circuit breaker operating mechanism often includes a crossbar unit that is operatively coupled to the movable contact and arranged to rotate or otherwise move the moveable contacts between the ON and OFF conditions. Several components associated with crossbar operation are required to maintain proper positioning of the crossbar and to ensure that the rotation of the crossbar is limited to a predetermined rotational travel distance. The associated components undesirably impart a high degree of friction on the crossbar, such that tripping of the circuit breaker is longer in duration than a crossbar that experiences lower friction. Therefore, the number of necessary components and the associated frictional forces are undesirably high. Often, grease or other lubricant is required to be applied to the crossbar and supports, increasing costs. It thus would be desireable to provide a circuit breaker having fewer operating mechanism parts that can provide a more rapid tripping response.